Driving Curve
We could tell you that Driving Curve is like Nike+ for driving, but as it turns out, the developers already did that for us. So instead, we'll tell you that this free app uses GPS to capture your speed and evaluates your performance based on how much it varies. And just like Nike+, it also gives you a score based on how you do, doles out achievements when you hit certain goals, and lets you share and compare results with both friends and other drivers from around the world. So, basically, the biggest difference is you don't have to stick a sensor into a hole in your tires for it to work.
